Motor control system



April 25, 1933.

W.. F. EAMES MOTOR coNTRoLsYsTEM Filed Feb.

INVENTOR ATTORNEY Patented pr. 25, 1933 `UNITED STATES PATENT oFFlcE WILLIAM F.

ELECTRIC EAMES, OF EDGEWOOD, PENNSYLVANIA, ASSIGNOR T WESTINGHOUSE & MANUFACTURING COMPANY, A COBPORATIONYOF PENNSYLVANIA Moron coN'rnoL sysrmr Application led February 15, 1930. Serial N0. 428,650.

My invention relates to motor control systems, and has particular relation to motor control systems of the variable voltage type in which the motor armature is connected in a closed circuit with the armature'of a variable voltage generator, 'the speed of the motor being determined by the generator excitation, and the direction of motor rotation being determinedv by suitable revers ing switches in any desirable circuit of the system, preferably in the generator field circuit.

In such systems, as ordinarily constructed, the motor is acceierated by short circuiting steps of resistance in the generator separately excited iield circuit, the time constant of the generator separately excited field circuit being relied upon to determine the rate of increase or decrease of the generator volt age and consequentiy of the motor speed. lVhile for many. purposes such systems are reliable and satisactory7 they are not entrely suitable for applications which require uniform acceieration and close speed regulation, suclias elevator systems.

The speed regulation of such a system is inherently peor., due to the resistance drop in the armatures oi' the generator and motor and in the conductors connecting them and also due to the speed regulation o the generator driving means. if the generator is provided with a cumulative series field winding of suiicient number of turns to compensate for the resistance drop in the common circuit of the motor and generator armatures and for 'the speed regulation of the generator driving means, the speed of the motor may be held substantially constant regardless of the load. However, the teniperature and consequently the resistance of the generator and motor armatures does not remain constant during operation but varies considerably. if the. generator series field is designed tc maintain the motor s eed constant while the machines are cold, t e motor speed regulation will assume a drooping characteristic as the machines heat up.. If on the other hand the generator series field is designed to maintain the motor speed constant While the machines are at an average Working temperatureor at a maximum working temperature, the motor speed will rise with increase of load when the machines are cold. A rising speed characteristic is particularly objectionable as motor operation under such conditions is unstable, erratic and diiiicuit to control.

In such a system as that described, in which the time constant of the enerator separately excited eld circuit is re ied upon to determine the rateof acceleration of the motor, adjustment of the motor acceleration characteristics to suit the requirements of a particularinstalla-tion, cannot alwa s be carried to as ne a degree as desirab e. The time constant of the generator separately excited field circuit does not remain the seme during the entire yacceleration period, but changes with each change of resistance in the eld circuit, so that if the average rate of change of generator excitation is at a desirable vaiue during a particular interu val in the acceleration periody it will not remain at this desirable value during other intervals when the resistance of the eld circuit is of a diierent value. Furthermore, the time constant ci the generator eld circuit can oniy be altered within certain limits determined by the design of the generator and the voit/ages avaliable for the generator field circuit.

it is accordingly an object of iny inven-y tion to provide a variable Voltage motor control system in which the acceleration and deceleraticn of the motor are independent of the time constant of the generator eld.

Another obiect of my invention is to provide a variable voltage motor control systeni in which the period of acceieration and deceleration oi the motor may be adjusted over a Wine range.

Another object of my invention is to prfvide e Variabile Voltage motor control system in which. means are provided for maintaining' the motor speed constant9 indegendent of variations ci load, and in which the motor speed regulation is independent of changes in temperature of the generator and motor armatures.

AAccording to my invention I control the speed of the motor in accordance with the difference between the volt es of an auxiliary variable voltage sup iliary generator drlven om the motor shaft, so that the motor speed is held at a value determined by the voltage of the auxiliary source, regardless of variations in the motor load or of variations in temperature of the main generator or motor during operation.

` Gther objects of my invention will become evident from the following detailed description, taken in conjunction with the accompanying drawing, in which the single fleure 1s a diagrammatic view of a system or control organized in accordance with the present invention.

Referring to the drawing a direct current motor M, the operation oi which is to be controlled, has its armature M connected in a closed circuit with the armature G of a direct current main generator' G. A pair of supply conductors L1 and L2 are provided for supplying the direct current used in the control system. The supply conductors L1 and L2 are energized from any suitable supply source, such as an exciter E, mounted on the shaft of the main generator G. The main generator G and exciter E are driven at substantially constant speed by any suitable driving means DM. A separately-excited-field winding Gf for the generator G is arranged to be connected to the suppl conductors L1 and L2 in series relation with a resistor r2 by either of a pair of reversing switches 1 and 2. Each of the reversing switches 1 and 2 carries a set of auxiliary contact members la: and 2a. respectively for connecting a resistor R to supply conductors Ll and L2 when either reversing switch 1 or 2 is closed. A` circuit comprising the armature 7 of an auxiliary generator 7 and the moving coil 8o and the stationary coil 8b of a regulator 8 is connected potentiometer fashion7 to an intermediate point 18 of the resistor R. The field Winding 7 of the auxiliary generator 7 is connecte in parallel relation to the circuit comprisin the main generator separately excited fiel winding Gf and the resistor r2, so that its polarity will be reversed When the main generator field is reversed.

The regulator 8 may be of any type, but is referably of the movin coil type, de.- scribed in the copending app ication of Walter Schaelchlin, Serial No. 221,422, filed September 23, 1927, (W. E. Case 12,060),

f and assigned to the Westinghouse Electric and Manufacturing Company. This regulator comprises a magnetic structure 8a having a core 8c' on which is mounted a stationary coil 8b. A pivoted'armature 8g of nonma etic material carries a movable coil 8c auf a movable contact member- 8d. The

movable coil 8c is arranged in inductive rey and an aux-` lation to the magnetic structure 8a, as is the stationary coil 8b. The movable contact member 8d is arranged to engage a stationary contact member 8f in one position of the armature, or to engage a second stationary contact 'member 8e 1n another position tact member 8f. The contact members 8d,

8c and 8f are so connected to the external circuit that when contact' member 8d engages contact member 8f, the resistor 72 in the main generator separately excited field circuit is short-circuited to increase the generator excitation, and when the Contact member 8d engages the contact member 8e, the resistorr1 is connected in shunt to the main generator field winding Gf to reduce the generator excitation. A condenser Cz' is connected between the contact members 8d and 8e to reduce sparking at the regulator contact members, and a similar condenser C2 for a similar purpose is connected between the contact members 8d and 8f.

The resistance values of resistors r1 and 12 is so related to the inductance of the generator field windin Gf and lthe voltage of supply conductors 1 and L2 that the excitation of the main generator G may be varied rapidly by the regulator 8 at any point in the entire working range.

A plurality of accelerating relays 3, 4, 5 and 6 are arranged to short-circuit adjustable portions o resistor R when they are de-ener ized and to remove the short. circuits wen they are energized, the arrangement being such that as the relays 3, 4, 5 and 6 are successively energized, the voltage applied to the circuit including the auxiliary generator armature 7 and the coils of regulator 8 by the potentiometer connection is increased.

Each of the relays 3, 4, 5 and is subject to inductive time delay in closing because of the inductance and resistance of its respective operating windin 3c, 40, 5c or 6c. A resistor r3, 14, 15 or r6 or each relay is connected in parallel to the operatingc coil 3c, 4c, etc., for introducing an inductive time delay in the o ning of the relay. The relays 3, 4, 5 an 6 may also be provided with demagnetizing windmgs 3d, 4d, 5d and 6d respectively, designed to set up a flux of small value in opposition to the flux of operating coils 3c, 4c, etc., to eliminate the ef'- fects of residual magnetism when the operating coils are (1e-energized and also to permit an adjustment of the time elements of the relays.

The r'ela s 3, 4, 5 and 6 are divided into groups, eac group being operatedvselectively from `a contact member of a manual controller 9 to bring the motor up to a predetermined speed. While for simplicity I.

have shown only two groups of two relays each, one group comprising relays 3 and 4 and the other comprisin relays 5 and 6, in practice a larger num er of groups and a different number of relays in each group would be used, the total number of relays being determined roughly by desired acceleration period of the motor. I have found, for example, that a particular type of relay operates satisfactorily in the above arrangement with a time element of ap roximately .2 of a secondD Using rela-ys o this type in an installation in which it is desired to accelerate the motor in ,approximately 2.8 seconds, 14 relays would be used, divided into groups according to the value and number of motor speeds desired.

The first relay of eachgroup (8, 5) is controlled from a contact member of the manual controller 9, each succeeding relay (4, 6) of a group being operated by contact members of the relay (3, 5) in the same group next preceding it in closing sequence, the first relay of each succeeding group except the last being controlled also by contact members of the 'last relay 6 of the group next following a closing sequence. In the arrangement shown the closing sequence of the accelerating relays is 3, 4, 5, 6 and the opening sequence is 5, 6, 3, 4.

The operation of the above described apparatus may be set forth as follows: Assuming that the main generator G and exciter E are being driven by their common driving means DM and the manual controller 9 is centered, the supply conductors L1 and L2 are energized, the field winding Mf of the main motor lvl is energized, the reversing switches 1 and 2 and accelerating relays 3, 4, 5 and 6 are all (le-energized, the eld winding Gf of the main generator and the field winding if of the auxiliary generator are disconnected, the resistor R is disconnected, and the motor M and auxiliary generator 7 are at rest.

If the handle of the manual controller 9 is moved in a counter-clockwise direction, Contact segment 8s of the controller bridges contact members 9m and 9b, completing a. circuit for the operating winding of reversing switch 1. This circuit may be traced from supply conductor L1 through conductor 10, contact members 9a, 9s and 9b of the controller 9, conductor 11, the operating coil of reversing switch 1, conductor 14 to supply conductor L2. switch 1 closes, connecting resistor R to supply conductors L1 and L2 by closure of its contact members 1w, and completing circuits for the main generator field Winding Gf and Reversing Y auxiliary generator iield winding 7i by closure of its contactmembers 1b and 1c. The circuit for the main generator ield winding Gf, extends from supply conductor L1 through contact members 1b of reversing switch 1, the generator field winding Gf, contact members 8f and 8d of regulator 8, contact members 1c of reversing switch 1, and conductor 15 to supply conductor L2. The circuit for the auxiliary generator field winding 7i extends from supply conductor L1 through contact members 1b of reversing switch l, the auxiliary generator field Winding 7f, contact members 1c of reversing switch 1 and conductor 15 to supply conductor L2.l

The resistor R is now connected directly to the supply conductors L1 and L2, and, because of the potentiometer connection 18, -a low voltage is impressed upon the circuit incl'1ding the coils 8b and 8c of the regulater 8 and the armature of auxiliary geny erator 7 as the motor M and auxiliary generator 7 are, at this vtime, at rest, the auxiliary generator 7 generates no voltage, so that the low voltage mentioned above acts unopposed upon the regulator 8 to maintain the contact member 802 in engagement with the contact member 8f. The resistor r2 is, accordingly, maintained short circuited, to cause the full voltage of exciter E to be impressed on the generator field winding Gf.

r1`he excitation of the generator G now increases rapidly, motor M starts and increases in speed, while the auxiliary generator 7 develops an increasing voltage in opn position to the low voltage impressed upon the regulator 8 by the resistor R, until the voltage oi auxiliary generator 'l' exceeds the voltage between the connection 18 to the resistor R and the supply conductor L2 by an amount suliicient for the force on the moving coil 8c oi the regulator 8 to overcome the tension of spring 877,. ldhen this occurs the movable contact member '8d of regulator 8 disengages the stationary contact member 8f, inserting the resistor r2 inseries with the main generator field winding Gf. The excitation of generator G is now reduced, and the speed of main motor-M decreases slightly, permitting movable contact member 8d of the regulator 8 to reengage the stationary Contact member 8f. The movable v contact 8d of the regulator 8 thus vibrates, maintaining the speed of motor M substantially constant at a low speed value proportional to the sum of the voltage between the connection 18 to the resistor R and the supply conductor L2, and the voltage necessary of the regulator 8. 1 If the load is overhauling, the generator G first supplies power to the motor M until the motor M and its load are accelerated to low speed value, after to overcome the tension of spring 8h which the direction of poweris reversed and .When the motor has fu the motor M returns power to the genera-l tor G, the movable contact member 8d of the regulator vibrating against stationary contact member 8e to maintain the motor speed constant at the low speed value. If the load on the motor M or the resistance of the common circuit of the generator and motor armature changes, the regulator 8 acts to change the excitation .of generator G accordingly to maintain the motor speed constant. i l

If the handle of manual controller 9 is moved farther in a' counter-clockwise direction, contact segment 98 of controller 9 bridges contact members 9m and 9c completing a circuit for the o erating coil3c of accelerating relay 3. is circuit may be traced from supply conductor L1 through conductor 10, contact members 9a, 9s and 9c of controller 9, conductor 12, the operating coil 3c of accelerating rela 3 and conductor 14 to supply conductor 2. The current throu h the operating coil 3c now gradually builds up at a rate determined by the inuctance and resistance of the relay coil. At the expiration of a predetermined time interval relay 3 closes, removing a short circuit for a portion of resistor R by the opening of its contact members 3a and establishing a closing lcircuit for relay 4 by closure of its contact members 3b. This circuit may be traced from supply conductor L1 through conductor 16, contact members 3b of acceleratingrelay 3, the operating coil 4c of accelerating relay 4, thence through conductor 14 to supply conductor L2. The current through the relay coil 4c now graduall builds up, and at the expiration of a pre etermined time interval the relay 4 operates, removing a short circuit from a second section of resistor R by the opening of its contact members 4a. The voltage between the connection 18 to the resistor R and the supply conductor L2 thus increases in increments at predetermined time intervals. Each increment of voltage acts momen tarily unopposed upon'the regulator 8 to cause engagement of the contact members 8d and 8f and the consequent short-circuiting of resistor r2. The voltage of generator G and the speed of motor M accordingly rise until the increasing voltage of auxiliary generator 7 equals the voltage impressed upon the regulator 8 by the resistor R. ly accelerated in response to closure of relays Sand 4, it opl erates at a 4constant intermediate speed.

If the handle of controller 9 is moved to the next operating int, a circuit is ccmpleted for the acce erating relay 5. This circuit extends from supply conductor L1, through conductor 10, contact members 9a,

9s and 9d of the manual controller 9, conductor 13, the operating coil 5c of accelerating relay 5 and conductor 14 to supply conmenait ductor L2. After the expiration of a predetermined time interval relay 5 closes, re-

moving a short circuit from a third section of resistor R by the opening of its contact members 5a, and closing a circuit for the operating coil 6o of relay 6 by the closure of the contact members 5b. This circuit may be traced from supply conductor L1, through conductor 16, contact members 5b, the operating coil 6c of accelerating re'la 6 and conductor 14 to supply conductor i2 After the expiration of a predetermined time interval accelerating relay 6 closes, removing a short circuit from a third section of resistor R b the opening of its contact members 6a an establishing' a holding circuit for relay 3 independent of the manual controller 9 by the closure of its contact members 6b. This circuit may be traced from supply conductor L1, throu h conductor 16, contact members 6b of rc la 6, conductor 11, the operating coil 30 o relay 3 and conductor 14 to supply conductor L2.

The removal of the short-circuits around sections of resistor R by the successive operation of accelerating relays 5 and 6 brings the speed of motor M up t'o full speed value. The motor M now operates at full s eed, its speed being held constant regar less of variations of load or of the temperature of the generator and motor armatures by the action of regulator 8.

If the handle of the manual controller 9 is now returned toward central position, the circuit of the operating coil 5c of relay 5 is broken at contact member 9d of the manual controller. The relay 5 does not immediately drop out, however, as the inductance of the relay coil maintains a momentar current through the resistor T5. After t e expiration of a predetermined time interval relay 5 drops out, short-circuiting a section resistor R and opening the circuit of the operating coil of relay 6. After the expiration of a predetermined time interval relay 6 drops out, short-circuiting a section of resistor' R and opening the holdin circuit for relay 3 at contact members 6 thereby preparing the circuit of relay 3 for control by the controller 9. The speed of motor M has now decreased to intermediate speed value.

If the handle of manual controller 9 is now returned further toward central position, the circuit of the operating coil 3c of relay 3 is broken at contact member 9c. After the expiration of a predetermined time interval, rela 3 drops out short-circuiting a section o resistor R and breaking the circuit of the operating coil 4c of relay 4. After a predetermined time interval relay 4 drops out short-circuiting a section of resistor R. The motor M now operates at low speed.

If the manual controller 9 is now centered,

the circuit of the operating coil of reversing switch 1 is broken at contact member 9b, the motor being brought to rest and the circuits restored to their original condition.

By adjusting the potentiometer connection 18 of the resistor R, the full speed value 'of the motor M may be varied. By adjustcoil by a predetermined amount, and drops out under similar conditions.

While I prefer to use a regulator of a specified type operating upon the generator separately excited field, because of the advantages of this arrangement, it Will be understood that my invention is not limited specifically to this arrangement. I may for example omit the spring 8h of the regulator 8, in which case the regulator 8 would o erate to maintain the dill'erence between t e voltages of the generator 7 and the potentiometer voltage (between 18 and L2) at a diierent predetermined value from the value maintained in the arrangement shown. If the spring 87e, is omitted, the predetermined value would be zero. Alternatively I may use an entirely diiferent type of regulator or may omit tbe regulator entirely. In the latter case a component of the excitation ci the main generator would be controlled directly in accordance with the difference between the voltages or enerator 7 and the potentiometer voltage.

'hile I preer to introduce 'the control in the generator field circut, because of the advantages'of this arrangement, I may introduce the control in other circuits of the sysm tem consistent with the desired result or maintaining the speed of the main motor proportional to the potentiometer voltage.

In my copending application Serial No. 428,647, filed February 15, 1930, I have disclosed a motor-control system' of the variable voltage type, in which the excitation of the generator supplying the Work motor is controlled by a regulator responsive to, the did'erences of voltages or an auxiliary generator driven at variable speed and a second auxiliary generator driven by the Work motor, in such manner as to eliminate- -A the effect of load upon the speed of the Work motor.

In my copending application Serial No. 428,648, filed February 15, 1930, I have disclosed a variable voltage motor-control system, in which the excitation of the generator supplying the work motor is controlled and an auxiliary motor, in such a manner as to eliminate the ell'ect of load on the speed of the work motor, and in which the speed and rate of change of speed of the auxiliary motor may bc independently controlled,

' In my copending application Serial No. 445,303, iled April 18, 1930, I have disclosed a variable voltage motor-control system, in whch'the excitation of the generator supplying the work motor is controlled in accordance with the difference between the counter-electromotive force of the Work motor and the voltage of an auxiliary generator driven at constant speed, in such a manner as to eliminate the effect of load upon the speed of the Work motor.

. In my copending application Serial No. 445,304, filed April 18, 1930, I have disclosed a variable voltage motor-control system, in which the excitation of the generator supplying the work motor is controlled in accordance with the counter-electromotive force of the Worlr motor, as measured by the terminal voltage of the generator corrected for armature resistance drop, in such a manner as to eliminate the eect oi load upon the speed of the Work motor.

In my copending application Serial No. 471,684, led July 30, 1930, I have disclosed an elevator system, in which the speed regulation of the elevator motor is corrected by means of a compounding arrangement and the rate of deceleration of the elevator inoecl tor is controlled by the time element means,

and in which a load responsive device is provided'- :for operating upon the time element means to obtain uniform deceleration under all load conditions..

In my copending application Serial No. 547,389, filed lune 2'?, 1931, have disclosed a variable voltage motor-control system, in which the excitation of the genera,- tor supplying the Work motor is controlled in accordance with the difference between the counter-electromotive force of the Worlt motor and the voltage of an auxiliary generator driven at variable speed, in suoli a manner as to eliminate the effect of load upon the speed of the Worx motor.

In the present application, I do not claim the control or the generator excitation broadly in accordance with a voltage proportional tothe did'erence between the actual speed of the motor and a predetermined control speed, as this is the subject matter of my application Serial No. 428,647, filed February 15, 1980, mentioned above.

In the present application, I do not claim the control of the generator excitation in accordance with the differential rotation of the Work motor, as compared with an inde* pendently driven rotary element, as this subject matter is claimed in my copending application Serial No.- 428,648, filed February 15, 1930, mentioned above.

In the present application, Ido not claim the control of the generator excitation by means responsive to a .control voltage, the terminal voltage of the motor, and a voltage proportional to the motor armature current, nor b means responsive to a control voltage an a voltage substantiall equal to the counter-electromotive force o the work motor, as this subject matter is covered in my copending application Serial No. 445,- 303, tiled Aprll 18, 1930, mentioned above.

I do not claim the control of the generator excitation broadly by means responsive to ythe terminal voltage of the motor and a voltage proportional to the motor armature current, nor broadly by means responsive to a voltage substantially equal to the motor counter-electromotive force, as tnis subject matter is claimed in my copendin application Serial No. 445,304, tiled Apr' 18, 1930, mentioned above.

In the present application, I do not claim the control of the rate of change of speed of an elevator motor by means including a load responsive element for correcting the motor speed regulation, means for determining the rate of change of speed of the elevator motor, and additional load responsive means for operating upon the last mentioned means to cause the rate of change of speed of the elevater motor to be the same under all load conditions, as this subject matter is claimed in my copending application Serial No. 471,- 684, led July 30, 1930, mentioned above.

I do not claim the control of the generi tor excitation by means responsive'to the counter-electromotive force of the motor and a voltage furnished by the specific means of a control generator driven at variable speed, nor to the control of the generat or excitation by means involving an auxiliary machine decelerated by the specific means of an electro-magnetic brake, as this subject matter is claimed in my copendin application Serial No. 547 ,389, mention above. y

I do not, therefore, wish to be restricted to the specific structural details, arrangement of parts or circuit connections herein set forth, as various modifications thereof may be effected without departing from the spirit and scope of my invention. I dire, t ereiore, that only such limitations shall be imposed as are indicated in the appended claims.

I claim as my invention:

1.111 a motor control system, 'a motor, a

generator, means for driving said generator, electrical connections' between the armatures of said motor -a'nd said generator means for impressing ka voltage upon a field winding of said genera r, means for regulating said voltage to 'cause thaspeed of said motor to be independent of load and for temporarily increasin said voltage above its final value-while' ghe motor is acoelerating to a corresponding speed, and means for controlling said last mentioned means to cause the spiced ofsaid motor to have successively hig er values at the expiration of successive intervals of time.

2. In a motor control system, a motor, a generator, means for driving said generator, electrical connections between the armatures of said'motor and said generator, a

field forcin resistor in the circuit of a fieldl winding o said generator, a circuit connected in shunt to said ristotr, contact members in said last mentioned circuit, means for closing saidl contact members while said motor is accelerating to a desired speed and for opening said contact members when the motor attains said desired speed, and means for controlling said last mentioned mcans to cause said desired speed to have successively higher values at the expiration of successive intervals of time.

3. In a motor control system, a motor, a generator, means for driving said generator, electrical connections between the armatures of ysaid motor land said generator, means for imprein a voltage upon the field winding of sai generator, means including a plurality of time element relays for changing the value of said voltage 1n increments at predetermined time intervals and means for simultaneously adjusting the time elements of said relays.

4. In a motor control system, a motor, a generator, means for driving said generator, electrical connections between theV armatures of said motor and said generator, an auxiliary voltage sup ly, means for causing the voltage of sai auxiliary sup ly to have successively higher values at t e expiration of successlve intervals of time, means for producingi a. voltage proportional to the speed of sai motor, and means responsive to the algebraic sum of the voltage of said auxiliary supply and said last meuf tioned means for controlling the excitation of said generator to maintain said sum at a predetermined value.

5. In a motor control system, a motor, a. main generator, means for driving said main generator, electrical connections between the armatures of said motor and said main generator, an auxiliary voltage source of time controlled relays for ortaircuiting portions of said resistor, a potentiometer connection to said resistor, an auxiliary generator, means for driving said auxiliary generatorvat a speed roportional to the vspeed of said motor andp algebraic sum of the voltages of said potentiometer connection and saidauxiliary generator for controlling the excitation of ,L izo resistor connected to said sourceila pluralityl means responsive to the I said main generator to maintain said sum at a redet-ermined value.

6. iii a motor control system, a motor, a main generator, means for driving said mai generator, electrical connections between the armatures of said motor .and said main generator, an auxiliary voltage source, a resistor connected to said source, a plurality of time element relays for short-circuiting portions of said resistor, said relays being divided into groups, a controller for operating a first relay of each group, means for operating the remaining relays of each ,group selectively after operation of said first relay,

a potentiometer connection to said resistor, an auxiliary generator, means for driving 'said auxiliary generator at a speed proportional to the speed of said motor, and means responsive to the algebraic sum of the voltages of said potentiometer connection and said generator lfor maintaining said sum at a predetermined value.

7. In a motor-control system, generator, means for driving said generator, electrical connections between the armatures of said motor and. said generator, a fieldforcing resistor in the circuit of a field winding of said generator, acircuit connected in shunt to' said resistor, contact members in said last mentioned circuit, an auxiliaryT voltage supply, means for producing a voltage proportional .to kthe speed of said motor and means, responsive to the algebraic sum of the voltages of said auxiliary supply and said last mentioned means, for maintaining said contact members closed while said motor is accelerating to a and for opening said contact members when said motor attains said predetermined speed.

8. In a motor-control system, amotor, a generator, meansfor driving said generator, electrical connections between the armatures of said motor and said generator, a circuit in shunt to a field Winding of said generator, contact members in said circuit, an auxiliary voltage supply, means for producing a voltage proportional to the speed of said motor and means, responsive to the algebraic sum of the voltages of said supply and said last mentioned means, for maintaining said contact members closed while said motor is decelerating to a predetermined speed and for opening said contact members when said motor attains said predetermined speed.

9. In a motor-control system, a motor, a generator, means for driving said generator, electrical connections between'the armatures of said motor and said generator, a fieldforcing resistor in the circuit of a field winding ofsaid generator, a circuit in shunt to said resistor, contact members in said last mentioned circuit, an auxiliary voltage supply, means for producing a voltage proportional to the speed of said motor and means,

a motor, a

predetermined speed responsive to the difference of the voltages of said auxiliary supply and said last mentioned means, for maintaining said contact members closed while said motor is accelerating to a predetermined speed and for opening said contact members when said motor attains said predetermined speed.

10. In a motor-control system, a motor, a generator, means for driving said enerator, velectrical connections between t e armatures of said motor and said generator, a circuit in shunt to a field windm of said generator, contact members in sai circuit, an auxiliary voltage supply, means :for producing a voltage roportional to the speed of said motor an means,res difference of the voltages of said supply and said last mentioned means, for maintaining said contact members closed while said motor is decelerating to a predetermined speed and for opening said contact members when said motor attains said predetermined speed.

11. In a motor control system, a motor, a generator, means for driving said enerator, electrical connections between t e armatures of said motor and said generator, a resistor in series with the field windin of said generator, a circuit in shunt to the eld winding of said generator, contact members in said circuit, means for operating said contact members, and means responslve to the speed ofsaid motor for controlling said last mentioned means to operate said contact members to complete said circuit when the actual speed of said motor exceeds a predetermined value and to operate said contact members to break said circuit whenthe actual speed Y of said motor is below value.

12. In a motor-control system, a motor, a generator, means for driving said enerator, electricalconnections between t e armatures of said motor and said generator means for impressing a voltage upon a field winding of said generator, field forcing means formantaining said voltage below the value corresponding to a desired speed of said motor while said motor is decelerating to said desired speed, means for rendering said field forcing means ineffective when said motor attains said desired speed and for said predetermined causing the speed of said motor to be independent lof load, and means for controlling said last mentioned means to cause the speed of said motor to have successively lower values at the expiration vals of time.

In testimony whereof, I have hereunto subscribed my name this 12th day of February, 1930. w

WILLIAM F. EAMES.

of successive inter- A 

